Liquified natural gas, known in German as “Flüssiges Erdgas” or referred to in abbreviated form as “LNG”, is natural gas which has been cooled to a temperature of −162° C. and has thereby taken on a liquid state. Nowadays a large number of natural gas sources are known of which are unfortunately a very long way away from the end-consumers. One cost-effective way of transporting natural gas over long distances is to liquify the natural gas and to transport it in tanker ships, also known as LNG-tankers. The liquid natural gas is transformed back into gaseous natural gas at the destination.
The document WO 2006/077094 discloses an apparatus as well as a method which make it possible to use the natural gas transported by the LNG-tankers as a source of fuel for driving the motors of the LNG-tanker. As described in detail in the document, a boil-off gas develops in the upper area of a storage tank which contains liquified natural gas. This boil-off gas is taken from the storage tank, then compressed and subsequently supplied to an engine on the ship, e.g. a combustion engine, as gaseous natural gas.